1. Field of Invention
This invention relates to the nondestructive measurement of the moisture content of individual single grain kernels, seeds, nuts, or fruits.
2. Description of the Prior Art
The moisture in cereal grains, seeds, nuts, and fruits is presently measured in bulk samples, and most of the available grain moisture meters are suitable for bulk samples only. The bulk values thus measured do not always represent the moisture content of every kernel in the bulk sample and do not provide any information on the range of moisture contents of the individual kernels within the sample. Kandala [M. S. Thesis, The University of Georgia, Athens, Ga. (1987)] reported earlier that single kernel moisture content in corn (maize), Zea mays L., can vary as much as .+-.0.8% on a wet basis (w.b.) from the bulk value as obtained by air-oven drying tests on single kernels and bulk samples from well-conditioned corn samples. Larger variations are expected in unconditioned samples. Grain with high levels of moisture, when blended with grain of permissible levels for safe storage, can be conducive to the growth of microorganisms and may lead to spoilage. Concern has developed that spoilage of grain in transit or storage may be related to the practice of blending (mixing) of grain lots of different moisture levels.
Nelson [J. Microwave Power 13 (2): 213-218 (1978)] investigated the moisture dependence of the dielectric constant of shelled, yellow-dent field corn (maize) at different frequencies from 1 MHz to 11 GHz. Relationships established between the dielectric constant and moisture content of corn from the experimental data are shown in FIG. 1.
Measurements of capacitance and dissipation factor of a small parallel plate capacitor with single kernels of corn between and in contact with the plates have shown promise for rapidly and nondestructively measuring the moisture content of single kernels. Kandala et al. [International Agrophysics 4 (1-2): 3-12 (1988)] measured the capacitance of a parallel plate capacitor, with and without a kernel of corn between the plates, at 1.0 and 4.5 MHz. These values were used along with the kernel weight, thickness, and projected area in an equation to predict kernel moisture content within .+-.1% moisture on 78 to 90% of the kernels measured from different lots in the moisture range from 11 to 24%. Later, another equation was developed [Kandala et al., Trans. ASAE 31 (6): 1890-1895 (1988)] which used the dissipation factor as well as capacitance values at the same two frequencies and eliminated the need for kernel thickness and capacitance of the parallel plates without the kernel. However, measurements of the weight and projected area of the kernel were still required. This equation enabled the prediction of moisture contents over a wider range (9.5 to 26%), and predicted the moisture contents for 89% of the kernels within .+-.1% of the air-oven values.
Electrical resistance of single kernels between crushing roller electrodes is also used for single kernel moisture measurement, but this is a destructive process.